1. Field of the Invention
The invention relates to the technical field of vehicle steering columns. Steering column conventionally means a tubular element, fixed to the body of the vehicle, under the dashboard, which guides and supports the drive shaft connected to the steering wheel.
This steering wheel is then a manual control member, connected to the steered wheels and used by the driver to steer the vehicle.
2. Description of the Prior Art
The invention also concerns decoupled steering columns. Unlike conventional steering columns, decoupled steering columns are not associated with a steering box converting the circular movement of the steering wheel into angular displacement of the steering rod which brings about turning of the wheels.
On the contrary, for these decoupled steering systems, there is no direct mechanical link between the steering wheel and the wheels resting on the ground, whether the vehicle is real or belongs to a simulation system.
This simulation can be for play purposes, connected with training in driving schools or perhaps connected with an interactive driving simulation for the requirements of motor vehicle manufacturers.
In such simulators, the restitution of forces at the steering wheel by virtue of a mechanism generating a load torque on the steering wheel according to the type of vehicle to be simulated, whether or not fitted with power-assisted steering, must take into account the driving conditions to be recreated.
Measurement of the torque applied to the steering wheel is consequently essential for providing a good simulation, in real time.
Measurement of the torque on the steering wheel shaft is also very important in servo-or power-assisted steering.
This is because initiation of the assistance depends notably on the torque applied by the driver on the steering wheel.
The torquemeter, or torque sensor, used in servo-steering outputs a signal indicative of the turning torque exerted by the driver on the steering wheel and therefore on the drive shaft of the vehicle steering column.
This signal is conventionally sent to a steering assistance computer which initiates the assistance, by controlling for example an electric motor, in the case of electric servo-steering.
The majority of torquemeters comprise a torsion bar.
Under isotropic linear elasticity, the torque exerted in terms of pure torsion on a solid cylindrical bar of circular section varies, for a given material, as a function of the fourth power of the diameter of the bar, at a fixed angle of torsion.
Consequently, the fact of making an area of reduced cross section in the steering column allows a concentration and amplification of torsional deformation in this area, used for measuring the torque, to the detriment of the rigidity and mechanical strength of said torsion bar.
Examples of torsion bar torquemeters for servo-steering can be found in the following documents:
WO-97 08 527, EP-453 344, EP-325 517, FR-2 738 339 originating from the applicant,
as well as in the following other documents:
patent applications in Japan published under numbers JP-43 17 862, JP-50 77 743, JP-57 19 81 71, JP-59 07 58 64, JP-57 08 77 62, JP-59 11 85 77, JP-61 14 674, JP-62 13 43 71, JP-62 09 44 70, JP-63 29 037, JP-63 09 36 73, JP-30 79 473;
European patents published under numbers EP-369 311, EP-396 895, EP-418 5 763, EP-515 052, EP-555 987, EP-562 426, EP-566 168, EP-566 619, EP-652 424, EP-638 791, EP-673 828, EP-681 955, EP-728 653, EP-738 647, EP-765 795, EP-738 648, EP-770 539, EP-802 107;
PCT international patent applications published under numbers 87/02 319, WO-92/20 560, WO-95/19 557, WO-96/06 330;
patent applications in France, the United Kingdom and the United States published under the following numbers: GB-2 306 641, FR-2 705 455, U.S. Pat. Nos. 4,874,053, 4,907,668, 4,984,474, 5,123,279, 5,394,760, 5,515,736, 5,578,767, 5,585,573, 5,616,849, 5,641,916.
Torsion bar torquemeters are large in size. Their installation requires two additional bearings to lessen notably spurious flexion effects.
The document FR-2 724 018 relates to a torque sensor comprising an elongation measurement gauge device. This gauge device is disposed on a measuring body, subject to mechanical tensions under the action of a torque.
The document EP-442 091 describes an installation for measuring the angle of rotation or the torque of a rotary or fixed element of a machine, having a torsion element in the form of a spoked wheel connected to a number of measuring elements, at least one spoke of the spoked wheel being cut so that the parts of the spoke or spokes are applied one against the other upon the displacement by a predetermined flexion of the other spokes. The measuring device uses eddy currents.
The invention relates to a torque measurement system not having the drawbacks of the systems known in the prior art for steering columns and capable of being installed, possibly reversibly, at any point on the steering column, this device being insensitive to electromagnetic interference and being rigid, consisting of a single piece, with high inertia and of small size and low cost.
To that end, the invention relates to a vehicle steering column comprising a manual control member for applying a torque on the drive shaft of the column, said column being provided with means for measuring the torque applied to said drive shaft, said measuring means comprising a sensing element with no torsion bar placed along the axis of the drive shaft and producing a break therein.
In one embodiment, the column is of the decoupled type.
In another embodiment, the column has a steering box converting the rotating movement of the drive shaft into angular displacement of the steering rod which brings about turning of the wheels.
The column has assistance means whose initiation depends notably on the torque applied to the drive shaft by operation of the control member.
Assistance calculation means are provided, sending signals to the means for controlling the assistance means, depending on the turning torque applied to the drive shaft.
The means for measuring the torque applied to the drive shaft are formed from an assembly having a certain rigidity comprising:
a displaceable first outer ring;
a second outer ring, substantially unstressed, placed at a distance from the displaceable outer ring;
an inner ring immovably attached rotation-wise to a column on which the torque to be measured is applied, the displaceable outer ring being capable of being immovably attached rigidly to the means applying the torque to be measured on the column, the displaceable outer ring being assembled with the inner ring by at least one elastically deformable means;
the substantially unstressed outer ring being assembled with the inner ring by at least one substantially unstressed means;
the sensor comprising means of measuring the small relative displacement of the displaceable outer ring with respect to the substantially unstressed outer ring when a torque is applied on the column by the means.
Other objects and advantages of the invention will emerge during the following description of embodiments, a description which will be given with reference to the accompanying drawings, in which: